Oxidation-resistant lubricating composition



United States Patent 3,190,833 OXWATIUN-RESISTANT LUBRI'CATENG COMRDSITION Alan Rhodes, Willoughby, Ghio, assignor to The Luhrizol Corp, Wickihte, Ohio, a corporation of Ohio N0 Drawing. Filed Apr. 14, 1961, er. No. 102,933 12 Claims. (Cl. 252-327) This invention relates to an oil-soluble phosphorothioate composition and to a process for preparing the same. In a more particular sense this invention relates to a phosphorothioate composition having improved oxidation-inhibiting properties. The phosphorothioate composition of this invention is useful as an additive in hydrocarbon oils, especially lubricating oils.

Metal phosphor-odithioate are useful as oxidation-inhibiting additives in hydrocarbon oils. Despite their efficacy under ordinary service conditions, however, such phosphorodithioates are not entirely satisfactory for use in lubricating compositions which are subjected for prolonged periods to extremely severe service conditions. It is therefore desirable to improve the oxidation-inhibiting properties of metal phosphorodithioates. Methods known in the art for such improvement unfortunately have resulted also in an undesirable alteration of other properties of the metal phosphorodithioates, especially with respect to their foam-causing characteristics and oilsolubility.

It is accordingly an object of this invention to provide improved oxidation-inhibiting compositions.

I It is another object of this invention to provide a process for preparing improved oxidation-inhibiting compositions.

It is also an object of this invention to provide lubricant additives having desirable lubricating properties.

It i also an object of this invention to provide hydrocarbon oils having improved oxidation-inhibiting properties.

It is another object of this invention to provide lubricating compositions having improved oxidation-inhibiting and lubricating properties.

These and other objects are attained in accordance with this invention by providing a lubricating composition containing from about 0.01% to about 3.5% by weight of an oxidation-inhibiting agent prepared by a process comprising treating an oil-soluble Group 11 metal phosphorodithioate with up to about 0.75 mole of an epoxide.

The oil-soluble metal phosphorodithioates from which the improved oxidation-inhibiting agents of this invention are derived are the salts of metals in Group II of the Periodic Table and comprise preferably the salts of calcium, barium, strontium, zinc, and cadmium with phosphorodithioic acids having the formula wherein R and R are substantially hydrocarbon radicals such as alkyl, alkaryl, arylalkyl, and cycloalkyl radicals and contain a total of at least about 7.6 aliphatic carbon atoms per atom of phosphorus. They include, for example, the Group 11 metal phosphorodithioates de scribed in US. Patents 2,680,123; 2,689,220; 2,364,283; 2,364,284; 2,261,047; 2,329,436; 2,344,393; 2,368,800; 2,386,207; 2,388,199; Re. 22,830; Re. 22,829; and 2,838,535. The zinc and barium phosphorodithioates are particularly effective as additives in lubricating compositions and are therefore preferred for use herein.

The above limit with respect to the minimum number of aliphatic carbon atoms in R and R radicals per phosphorus atom is based primarily upon the solubility of the metal phosphorodithioates, i.e., those prepared from phos- 3,i%,833 Patented June 22, 1%65 ice phorodithioic acids in which R and R contain a total of less than about 7.6 aliphatic carbon atoms are not sufficiently soluble in lubricating oil to be useful as additives. For reasons of economy the substantially hydrocarbon radicals in the phosphorodithioic acids are preferably low or medium molecular Weight alkyl radicals and lower alkylphenyl radicals, i.e., those having up to about carbon atoms in the alkyl radicals. Illustrative lower alkyl radicals include methyl, ethyl, isopropyl, isobutyl, n-butyl, sec-butyl, n-pentyl, neopentyl, 3-methylbutyl, n-heptyl, methyl-isobutyl, Z-ethyl-hexyl, di-iso-butyl, iso-octyl, and decyl. Illustrative cycloalkyl radicals and alkylphenyl radicals include cyclopentyl, cyclohexyl, methyl-cyclohexyl, butylphenyl, amylphenyl, diamylphenyl, octylphenyl, and polyisobutyl (molecular weight 1000)-substituted phenyl. Other hydrocarbon radicals such as tetradecyl, octadecyl, eicosyl, butyl naphthyl, hexylnaphthyl, cyclohexylphenyl, and naphthenyl, likewise are useful. Many substituted hydrocarbon radicals such as 3-bromobutyl, chloroethyl, dich orophenyl, and p-chloromethyl-phenyl radical may also be used.

The availability of the phosphorodithioic acids from which the metal salts are prepared is well known. They are prepared, for example, by the reaction of phosphorus pentasulfide with an alcohol or a phenol. The reaction involves 4 moles of the alcohol or phenol per mole of phorsporus pentasulfide and may be carried out within the temperature range from about C. to about 200 C., preferably from about C. to about 120 C. Thus, the preparation of di-n-hexylphosphorodithioic acid involves the reaction of phosphorus pentasulfide with 4 moles of n-hexyl alcohol at about 100 C. for about 2 hours. Hydrogen sulfide is liberated and the residue is the defined acid. The preparation of the metal salt of this :acid may be effected by reaction of the acid with a metal neutralizing agent such as zinc, zinc oxide, or barium oxide. Simply mixing and heating these reactants is sufiticient to cause the neutralization to take place and the resulting product is sufficiently pure for the purpose of this invention.

Especially useful metal phosphorodithioates can be prepared from phosphorodithioic acids which in turn are prepared by the reaction of phosphorus pentasulfide with mixture of alcohols. The use of mixtures of alcohols enables the utilization of cheaper alcohols which by themselves do not yield oil-soluble phosphorodithioate acid salts. Thus, a mixture of isopropyl and hexyl alcohols can be used to produce a very ettective oil-soluble metal phosphorodithioate. For the same reason mixtures of simple acids i.e., acids prepared from a single alcohol, can be reacted with the metal neutralizing agent to produce less expensive oil-soluble metal salts.

-The epoxides useful in the above process are for the most part hydrocarbon epoxides and substantially hydrocarbon epoxides. The hydrocarbon epoxide may be alkylene oxides or aryl-alkylene oxides. The aryl alkylene oxides are exemplified by styrene oxide, p-ethylstyrene oxide, alpha-methylstyrene oxide, 3-beta-naphthyl-1,3-butylene oxide, n-dodecylstyrene oxide and p-chlorostyrene oxide. The alkylene oxides include principally the lower alkylene oxides, i.e., those having 6 or less carbon atoms in the alkylene radical. Examples of such lower alkylene oxides are ethylene oxide, propylene oxide, 1,2-butene oxide, trimethylene oxide, tetramethylene oxide, butadiene mono-epoxide, 1,2-hexene oxide, and 2,3-butene oxide. Higher alkylene oxides are illustrated by 1,2-decene oxide, epoxidized terpolymer of 95 parts (by weight) of isobutene with 3 parts of butadiene and 2 parts of styrene (having a molecular weight of 2000), epoxidized heptadecene, and epoxidized copolymer of parts of isobutene with 10 parts of isoprene having a molecular weight of 5000. The substantially hydrocarbon epoxides areas-ea may contain a polar-substituent. The polar-substituent is usually a halo radical such as chloro, fluoro, bromo, or iodo; an ether radical such as methoxy, decyl-oxy, or phenoxy; or an ester radical such as carbomethoxy, or carbobutoxy radical. Examples of such epoxides are epichlorohydrin, butyl 9,10-epoxystearate, epoxidized soy bean oil, and epoxidized tung oil.

The improved oxidation-inhibiting composition of this invention is obtained simply by mixing the metal phosphorodithioate and the epoxide. The reaction is usually exothermic and may be carried out within wide temperature limits from about C. to about 300 C. Because the reaction is exothermic it is best carried out by adding one reactant, usually the epoxide, in small increments to the other reactant in order to exercise convenient control of the reaction temperature. The reaction may be carried out in a solvent such as benzene, mineral oil, naphtha, or n-hexane. In some instances the reactions may be effected at a temperature below 0 C. such as l0 C. or -25 C.

A critical aspect of this invention is the upper limit of the relative amount of epoxide with respect to the amount of metal phosphorodithioate to be used in the above process. Such upper limit is 0.75 mole of an epoxide for each mole of the metal phosphorodithioate. The *limit is based primarily upon a consideration of the properties of the products resulting from the process. Thus, an important consequence of the use of an amount of the epoxide below such limit is that the oxidation-inhibiting property of the metal phosphorodithioate is improved. On the other hand, the use of excessive amounts of the epoxides, i.e., above such upper limit, appears to result in products which are no better, as regards oxidation inhibition than the metal phosphorodithioates, and which promote excessive foaming of lubricating compositions; furthermore, such products appear to have a limited oilmiscibility. Although the use of any amount of the epoxide below the above upper limit produces an improved oxidation-inhibiting composition, a particularly pronounced improvement is usually observed when at least 0.1 mole of the epoxide is used for each mole of the metal phosphorodithioate. Also, compositions obtained by the reaction of one mole of the phosphorodithioate with from about 0.25 mole to about 0.5 mole of a lower alkylene oxide have been found to be especially effective and therefore are preferred.

This invention contemplates also the presence of other additives in combination with the phosphorodithioate additive in lubricating compositions. Such additives include, for example, detergents of both ash-containing and ashless types, viscosity index improving agents, pour point depressing agents, anti-foam agents, extreme pres sure agents, rust inhibiting agents, and supplemental oxidation and corrosion inhibiting agents.

The ash-containing detergents are exemplified by oilsoluble neutral and basic salts of alkali or alkaline earth metals with sulfonic acids, carboxylic acids, or organic phosphorus acids characterized by at least one direct carbon-to-phosphorus linkage such as those prepared by the treatment of an olefin polymer (e.g., polyisobutene having a molecular weight of 1000) with a phosphorizing agent such as phosphorus trichloride, phosphorus heptasulfide, phosphorus pentasulfide, phosphorus trichloride and sulfur, white phosphorus and a sulfur halide, or phosphorothioic chloride. The most commonly used salts of such acids are those of sodium, potassium, lithium, calcium, magnesium, strontium, and barium. The term basic salt is used to designate the metal salts wherein the metal is present in stoichiometrically larger amounts than the oragnic acid radical. The commonly employed methods for preparing the basic salts involve heating a mineral oil solution of an acid with a stoichiometric excess of a metal neutralizing agent such as the metal oxide, hydroxide, carbonate, bicarbonate, or sulfide at a temperature above 50 C. and filtering the resulting mass.

The use of a promoter in the neutralization step to aid the incorporation of a large excess of metal likewise is known. Examples of compounds useful as the promoter include phenolic substances such as phenol, naphthol, alkylphenol, thiophenol, sulfurized alkylphenol, and condensation products of formaldehyde with a phenolic substance; alcohols such as methanol, 2-propanol, octyl alcohol, Cellosolve, carbitol, ethylene glycol, stearyl alcohol, and cyclohexyl alcohol; amines such as aniline, phenylenediamine, phenothiazine, phenyl-beta-naphthylamine, and dodecylamine. A particularly effective method for preparing the basic salts comprises mixing an acid with an excess of a basic alkaline earth metal neutralizing agent, a phenolic promoter compound, and a small amount of water and carbonating the mixture at an elevated temperature such as 60-200 C.

The ashless detergents are exemplified by the interpolymers of an oil-solubilizing monomer (e.g., decyl methacrylate, vinyl decyl ether, or high molecular weight olefin) with a monomer containing a polar substituent (e.g., amino-alkyl acrylate or poly-(oxy-ethylene)substituted acrylate); the amine salts, amides, and imides of oilsoluble monocarboxylic or dicarboxylic acids such as stearic acid, oleic acid, tall oil acid, and high molecular weight alkyl or alkenyl-substituted succinic acid. An especially useful ashless detergent is an acylated amine prepared by a process which comprises mixing a high molecular weight substantially aliphatic hydrocarbon (having at least about 50 aliphatic carbon atoms)-substituted succinic acid or anhydride with an ethylene amine (e.g., ethylene diamine or tetraethylene pentamine), heating the mixture to etfect acylation and removing the water formed thereby. The hydrocarbon radical in the substituted succinic acid or anhydride is most commonly derived from polymers of lower aliphatic olefins such as isobutene, propylene, or ethylene. The temperature for effecting the acylation is usually above C., preferably about l50200 C. The acylated amines and the method for the preparation of the acylated amines are described in greater detail in co-pending application Serial No. 802,667, filed June 3, 1960.

Extreme pressure addition agents are exemplified by chlorinated aliphatic hydrocarbons such as chlorinated wax; organic sulfides and polysulfides such as benzyl disulfide, bis-(chlorobenzyl) disulfide, dibutyl tetrasulfide, sulfurized sperm oil, sulfurized methyl ester of oleic acid, sulfurized alkylphenol, sulfurized dipentene, and sulfurized terpene; phosphosulfurized hydrocarbons such as the reaction product of a phosphorus sulfide with turpentine or methyl oleate; phosphorus esters including principally dihydrocarbon and trihydrocarbon phosphites such as dibutyl phosphite, diheptyl phosphite, dicyclohexyl phosphite, pentyl phenyl phosphite, dipentyl phenyl phosphite, tridecyl phosphite, distearyl phosphite, dimethyl naphthyl phosphite, oleyl 4-pentylphenyl phosphite, polypropylene (molecular weight 500)-substituted phenyl phosphite, di isobutyl substituted phenyl phosphite; metal thiocarbamates such as zinc dioctyl-dithiocarbamate, and barium heptylphenyl dithiocarbamate.

The oxidation-inhibiting agent of this invention is usually present in lubricating oils in amounts within the range from about 0.01% to about 3.5% by weight of the final lubricating composition. The optimum amount for a particular application depends to a large measure upon the type of service to which the lubricating composition is to be subjected. Thus, for example, lubricating compositions for use in gasoline internal combustion engines may contain from 0.1% to about 2% of the additive Whereas lubricating compositions for use in gears and diesel engines may contain as much as 3% or even more of the additive. On the other hand lubricating composi tions for use in 2-cycle out-board motor engines may contain as little as 0.01% or even less of phosphorus.

The lubricating composition of this invention may also contain detergent additives in amounts usually within nu-n the range from about 0.1% to about 20% by weight. In some applications such as in lubricating marine diesel engines the lubricating composition may contain as much as 30% of a detergent additive. They may also contain extreme pressure additive agents, viscosity index improving agents, and pour point depressing agents each in amounts usually within the range from about 0.1% to about by weight.

The lubricating oil base selected for the purposes of the present invention can be of synthetic, animal, vegetable, or mineral origin. Ordinarily the'mineral oils are preferred by reason of their availability, general excellence, and low cost, although for certain special applications oils belonging to one of the other three groups may be preferred. For instance, synthetic polyester oils such as, for example, didecyl adipate and di-2-ethyl hexyl sebacate, are often preferred for jet engine lubricants.

Normally the lubricating oils preferred for the purposes of the present invention will be fluid oils ranging in viscosity from about 40 Saybolt Universal seconds at 100 F. to about 200 Saybolt Universal seconds at 210 F. The invention also extends, however, to gelled oils or greases.

The following examples are illustrative of the process of preparing the oxidation inhibiting agent of this invention:

EXAMPLE 1 To 394 parts (by weight) of zinc dioctylphosphorodithioate having a phosphorus content of 7% there is added at 7585 C., 13 parts of propylene oxide (0.5 mole per mole of the Zinc phosphorodithioate) throughout a period of 20 minutes. The mixture is heated at 82-85 C. for one hour and filtered. The filtrate (399 parts) is found to contain 6.7% of phosphorus, 7.4% of zinc, and 4.1% of sulfur.

EXAMPLE 2 To 885 grams of a mineral oil solution containing 1 mole of zinc dioctylphosphorodithioate there is added 0.25 mole of propylene oxide at 75-85 C. The resulting mixture is heated at this temperature until reaction is substantially complete.

EXAMPLE 3 The procedure of Example 2 is repeated except that the quantity of propylene oxide used is 0.125 mole.

EXAMPLE 4 Propylene oxide, grams (0.26 mole) is added to 307 grams (0.4 mole) of zine di(4-methyl-2-pentyl)phosphorodithioate at 90-100 C. within a period of 1 hour. The mixture is heated at this temperature for 6 hours and then heated to 90 C./ mm. and filtered. The filtrate has a phosphorus content of 7.5%, a sulfur content of 15.6%, and a zinc content of 8.14%.

EXAMPLE 5 EXAMPLE 6 The procedure of Example 5 is repeated except that the zinc phosphorodithioate used is a zinc salt (323 grams, 0.5 mole) of a phosphorodithioic acid prepared by the reaction of phosphorus pentasulfide with a mixture of 65% (by weight) of isobutyl alcohol and of primary-pentyl alcohol.

(-3 EXAMPLE 7 The procedure of Example 2 is repeated except that the zinc phosphorodithioate used is zinc di(p-heptylphenyl) phosphorodithioate.

The following examples are illustrative of the lubricating compositions of this invention (all percentages are by weight) EXJXMPLE A SAE 20 mineral lubricating oil containing 0.05% of phosphorus as the product or" 0.5 mole of propylene oxide with the zinc salt of a phosphorodithioic acid prepared by the reaction of phosphorus pentasulfide with an equimolar mixture of methyl alcohol and n-octyl alcohol.

EXAMPLE B SAE 30 mineral lubricating oil containing 0.1% of phoshorus as the product of the barium salt of di-n-nonylphosporodithioic acid with 0.75 mole of 1,2-butene oxide.

EXAMPLE C SAE 10W-30 mineral lubricating oil containing 0.075% of phosphorus as the product of zinc di-n-octylphosphorodithioic acid with 0.6 mole of epichlorohydrin.

EXAMPLE D SAE mineral lubricating oil containing 0.1% of 0.15% of the product of the zinc salt of an equimolar mixture of di-cyclohexylphosphorodithioic acid and di-isobutyl phosphorodithioic acid with 0.5 mole of ethylene oxide.

EXAMPLE E SAE 30 mineral lubricating oil containing 0.06% of phosphorus as the product of an equimolar mixture of zinc di-cyclohexylphosphorodithioate and zinc di-dodecylphosphorodithioate with 0.75 mole of 1,2-pentene oxide.

EXAMPLE F SAE 20W-30 mineral lubricating oil containing 0.05% of phosphorus as the product of barium di-heptylphenylphosphorodithioate with 0.1 mole of styrene oxide.

EXAMPLE G SAE 10W30 mineral lubricating oil containing 0.05% of phosphorus as the product of the cadmium salt of a phosphorodithioic acid prepared by the reaction of phosphorus pentasulfide with a mixture of 60% (mole) of p-butylphenol and 40% (mole) of n-pentyl alcohol with 0.5 mole of cyclohexene oxide.

EXAMPLE H SAE 50 mineral lubricating oil containing 0.1% of phosphorus as the product of the strontium salt of dihexylphosphorodithioate with 0.5 mole of propylene oxide.

EXAMPLE I SAE 10W-30 mineral lubricating oil containing 0.06% of phosphorus as the product of calcium di-n-octylphosphorodithioate with 0.5 mole of ethylene oxide and 1% of sulfate ash as barium mahogany sulfonate.

EXAMPLE I SAE 30 mineral lubricating oil containing 0.1% of phosphorus as the product of the zinc salt of a mixture of equimolar amounts of di-isopropylphosphorodithioic acid and di-n-decylphosphorodithioic acid with 0.5 mole of 1,2-hexene oxide, and 2.5% of sulfate ash as a basic barium detergent prepared by carbonating at C. a mixture comprising mineral oil, barium didodecylbenzene sulfonate and 1.5 moles of barium hydroxide in the presence of a small amount of water and 0.7 mole of octylphenol as the promoter.

aisaese 7 EXAMPLE K SAE 10W-30 mineral lubricating oil containing 0.075 of phosphorus as the product obtained by treating zinc di-n-octyl-phosphorodithioate with 0.5 mole of propylene oxide at room temperature, and of the barium salt of an acidic composition prepared by the reaction of 1000 parts of a polyisobutene having a molecular weight of 60,000 with 100 parts of phosphorus pentasulfide at 200 C. and hydrolyzing the product with steam at 150 C.

EXAMPLE L SAE mineral lubricating oil containing 0.075 of phosphorus as the product of zinc di-cyclohexylphosphorodithioate treated with 0.3 mole of ethylene oxide, 2% of a sulfurized sperm oil having a sulfur content of 10%, 3.5% of a poly-(alkyl methacrylate) viscosity index improver, 0.02% of a poly-(alkyl methacrylate) pour point depressant, 0.003% of a poly-(alkyl siloxane) anti-foam agent.

EXAMPLE M SAE 10 mineral lubricating oil containing 0.075% of phosphorus as the product obtained by heating zinc dinonylphosphorodithioate witn 0.25 mole of 1,2-hexene oxide at 120 C., a sulfurized methyl ester of tall oil acid having a sulfur content of 6% of a polybutene viscosity index improver, 0.005% of a poly-(alkyl methacrylate) anti-foam agent, and 0.5 of lard oil.

EXAMPLE N SAE mineral lubricating oil containing 0.05% of phosphorus as the product of zinc di-heptylphosphorodithioate with 0.5 mole or" 1,2-butene oxide, 0.5% of di-dodecyl phosphite, 2% of the sulfurized sperm oil having a sulfur content of 9%, a basic calcium detergent prepared by carbonating a mixture comprising mineral oil, calcium mahogany sulfonate and 6 moles oi calcium hydroxide in the presence of an equi-molar mixture (10% of the mixture) of methyl alcohol and n-butyl alcohol as the promoter at the reflux temperature.

EXAMPLE 0 SAE 10 mineral lubricating oil containing 0.07% of phosphorus as the product of zinc di-octylphosphorodithioate with 0.25 mole or" propylene oxide, 2% of a barium detergent prepared by neutralizing with barium hydroxide the hydrolyzed reaction product of a polypropylene (molecular weight 2000) with 1 mole of phosphorus pentasulfide and 1 mole of sulfur, 3 of a barium sulfonate detergent prepared by carbonating a mineral oil solution of mahogany acid, and a 500% stoichiometrically excess amount of barium hydroxide in the presence of phenol as the promoter at 180 C., 3% of a supplemental ashless detergent prepared by copolymerizing a mixture of 95% (weight) of decyl-methacrylate and 5% (weight) of diethylaminoethylacrylate.

EXAMPLE P SAE 80 mineral lubricating oil containing 0.1% of phosphorus as the product of zinc di-n-hexylphosphorodithioate with 0.5 mole of epichlorohydrin, 10% of a chlorinated paraffin wax having a chlorine content of 2% of di-butyl tetrasulfide, 2% of sulfurized dipentene, 0.2% of oleyl amide, 0.003% of an antifoam agent, 0.02% of a pour point depressant, and 3% of a viscosity index improver.

EXAMPLE Q SAE 10 mineral lubricating oil containing 0.075% of phosphorus as the product of 0.5 mole of propylene oxide with the zinc salt of a phosphorodithioic acid prepared by the reaction of phosphorus pentasulfide with an equimolar mixture of n-butyl alcohol and dodecyl alcohol, 3% of a barium detergent prepared by carbonating 8 a mineral oil solution containing 1 mole of sperm oil, 0.6 mole of octylphenol, 2 moles of barium oxide, and a small amount of water at 150 C.

EXAMPLE R SAE 20 mineral lubricating oil containing 0.07% of phosphorus as the product of zinc di-n-octylphosphorodithioate with 0.25 mole of propylene oxide.

EXAMPLE S SAE 30 mineral lubricating oil containing 0.1% of phosphorus as the product of zinc di-(isobutylphenyl)- phosporodithioate with 0.4 mole of epichlorohydrin.

EXAMPLE T SAE 50 mineral lubricating oil containing 0.15% of phosphorus as the product of zinc di-primary-pentylphosphorodithioate with 0.3 mole of styrene oxide.

EXAMPLE U SAE mineral lubricating oil containing 0.2% of phosphorus as the product of zinc di-dodecylphosphorodithioate with 0.25 mole of 3,4-hexene oxide.

The above lubricants are merely illustrative and the scope of the invention includes the use of all of the additives previously illustrated as well as others within the broad concept of this invention described herein.

The elfectiveness of the oxidation-inhibiting agents of this invention in a lubricating composition is demonstrated by the results (summarized in Table I) of an oxidation test. The test consists of blowing air at a rate of 1.25 cubic feet per hour at 150 C. into 350 grams of a transmission lubricant having immersed therein an oxidation catalyst consisting of 125 grams of iron, 128 grams of copper, and 31 grams of lead until sludge is formed (as indicated by the appearance of haze or sediment). The lubricant used in the test comprises a mineral lubricating oil having a viscosity of 112 SUS (Saybolt Universal seconds) at F. and a viscosity index value of 85 and containing a basic barium detergent having a barium sulfate ash content of 35% (2.3% by volume, prepared by heating a mixture comprising 1000 parts (by weight) of sperm oil, 294 parts of heptylphenol, 2870 parts of mineral oil, 285 parts of water and 1540 parts of barium oxide to 300 F., carbonating the mixture at 275 F. until it is substantially neutral, and filtering the product), a basic barium sulfonate detergent having a barium sulfate ash content of 38.5% (0.92% by volume, prepared by heating a mixture comprising 805 parts (by Weight) of mineral oil, 625 parts of barium mahogany sulfonate, 210 parts of water, 146 parts of heptylphenol, and 740 parts of barium oxide to 295 F., carbonating the mixture at this temperature until it is substantially neutral, diluting the mixture with 520 parts of mineral oil, and filtering the product), a polymeric alkyl siloxane anti-foam agent (20 parts per million), and a commercial poly(methacrylate) viscosity index improving agent (3.64% by weight).

C Transmission lubricant+0.l% of phos- 70.

phorus as the product of zinc-di-primary-oetylphosphorodithioate with 2 moles of propylene oxide.

D Transmission lubricant+0.1% of phos- 96.

phorus as the product of zinc di-primary-octylphosphorodithioate with 0.5 mole of propylene oxide.

important advantage of the oxidation-inhibiting agents of this invention for use in lubricating compositions is their relative non-corrosiveness to metals. This advantage is shown by an ASTM Copper Corrosion Test 10 give a gear lubricant containing 4% by weight of the oxidati-on-inhib-iting agent.

Inasmuch as gear lubricant additives are often subj cted to high temperatures in service, it is important that (procedure designation ASTM 13130-56). The test conthe foam characteristics of the additives should not be sists of immersing a freshly polished copper strip in a impaired as a result of exposure to high temperature for lubricant, heating the lubricant at 300 F. for 3 hours, an extended period. Thus, the above concentrate after and measuring the extent of corrosion of the strip at the certain periods of storage at 150 F. is evaluated also by. end of the heating period. The measurement of corthe foam test. The results are reported in Table III. rosion is accomplished by comparing the strip with a set It will be noted that the foam resistance of the oxidationof ASTM copper strip corrosion standards and is reinhibiting agent of this invention (in lubricant sample ported on the following scale: 1 for slight tarnish; 2 for A) is significantly better than that of the corresponding moderate tarnish; 3 for dark tarnish; and 4 for corrosion. metal phosphorodithioate and the adduct of such phos- The results of the test are summarized in Table II. The phorodithioate with an excessive proportion of an epoxide.

Table 111 Volume of foam after storage Gear F. for-- lubricant Oxidation-inhibiting agent in lubricant sample 1 a 5% week week weks weeks A Adduet of zinc di-4-methyl-2-pentyl 0 110 phosphorodithioate with 0.5 mole of propylene oxide (Example 1). B

dit-4-methy1-2-pentyl phosphorodi- 0 320 320 103. e. C Adduct of zinc di-i-methyl-l-pentyl 220 350 310 phosphorodithioate with 1 mole of propylene oxide.

lubricant used in the test is a mineral base oil for Type A automatic transmission fluid containing 4.5% by volume of a commercial poly(acrylate) viscosity index improving agent.

The significance of the molar proportion of the epoxide in the oxidation-inhibiting agents of this invention is shown by an ASTM Foam Test (procedure designation D-892). The test procedure is as follows: A 180 ml. sample is placed in a 1000 ml. graduated cylinder, heated rapidly to 200:5 F., and then placed in a bath maintained at 75 F. When the oil sample reaches the bath temperature a current of air is bubbled through the sampic at the rate of 94:5 ml. per minute for five minutes. The volume in ml. of -air foam then is measured immediately and recorded. A volume of foam greater than about 150 ml. is regarded as an indication that the lubricant sample is undesirable.

The lubricant additive concentrate subjected to the foam test consists of 42 parts of the oxidation inhibiting agent, parts of an extreme pressure additive (chlorinated eicosane having a chlorine content of another extreme pressure additive (23 parts of a polysultide having a sulfur content of 48% acid derived from the reaction of iso'butene with sulfur monochloride and sodium sulfide), and 0.4 part of a commercial polymeric alkyl siioxane anti-foam agent. The concentrate is diluted before the foam test with SAE 90 mineral oil to The effectiveness of the oxidation-inhibiting agents of this invention in gear lubricants is shown further by an Axle Gear Test. The test consists of operating a ton Dodge military truck axle having an axle ratio of 5.8:1 first under high speed conditions and then under high torque conditions. The high speed conditions are: duration 100 minutes; axle speed, 440:5 r.p.m.; transmission gear level, fifth; load per axle shaft, 150:5 pounds; and maximum temperature, 300 F. The high torque conditions are: duration, 24 hours; temperature, 275 F.:3 F.; transmission gear level, second; load per each axle shaft 665:5 pounds; and engine speed, 1580 rpm. The gears used in the test have been treated With a commercial manganese phosphate composition. After completion of the test, the gears are inspected and the axle lubricant is said to pass the test if the surface gear teeth shows no visible distress, i.e., scoring, rippling, ridging, etc. A gear lubricant consisting of a SAE mineral lubricating oil containing 1.7% by weight of the adduct of zinc di-(4-rnethyl-2-pentyl) phosphorodithioate with 0.5 mole of propylene oxide, 1.4% by weight of a chlorinated eicosane having a chlorine content of 40%, and 0.017% by weight of a commercial polymeric alkyl siloxane an-tifoam agent is found to pass this test (in duplicate).

The lubricating compositions of this invention have been evaluated further by the Powerglide Transmission Lubricant Test. In this test, the lubricating composition is used in a 1955 Powerglide transmission operated under the following conditions: transmission sump temperature, 275 F.; transmission speed, 1750-1800 r.p.m.; governor pressure, 55-70 p.s.i.; main line pressure, 85 p.s.i.; and test duration, 300 hours. The lubricant is evaluated in terms of (1) the amounts of varnish and sludge formed (rating scale of 0-50, 0 representing heavy varnish or sludge and 50 representing no varnish or sludge), (2) the appearance of black stain on the metal transmission parts as an indication of corrosion, and (3) Weight loss of the thrush Washer due to corrosion. The results are summarized in Table IV. A modification of the test consists of blowing air through the lubricant at a rate of 0.12 gram per minute throughout the test.

This modification increases the severity of the test and is used in evaluation of lubricant C of Table IV.

3.2 7. The lubricating composition of claim 1 characterized further in that the epoxide is an alkylene oxide.

What is claimed is:

1. A lubricating composition comprising a major amount of lubricating oil and from about 0.01% to about 3.5% by weight of an oxidation-inhibiting agent prepared by a process comprising treating an oil-soluble Group II metal salt of a phosphorothioic acid having the structural formula wherein R and R are substantially hydrocarbon radicals containing a total of at least 7.6 aliphatic carbon atoms per atom of phosphorus with from about 0.1 up to about 0.5 mole of an epoxide selected from the class consisting of alkylene oxides having up to about carbon atoms, arylalkylene oxides having up to about 6 carbon atoms in the alkylene radical, chlorostyrene oxides, epichlorohydrin, butyl 9,10-epoxy-stearate, expoxidized interpolymer of isobutene and butadiene, epoxidized, interpolyrner of isobutene and isoprene, epoxidized soy bean oil and epoxidized tnng oil.

2. The lubricating composition of claim 1 characterized further in that the Group II metal phosphorodithioate is a zinc phosphorodithioate.

3. The lubricating composition of claim 1 characterlzed further in that the Group II metal phosphorodithioate is a zinc dialkyl phosphorodithioate.

4. The lubricating composition of claim 3 characterized further in that each alkyl group in the zinc dialkylphosphorodithioate contains from 1 to about 30 carbon atoms.

5. The lubricating composition of claim 3 characterized further in that each alkyl group in the zinc dialkylphosphorodithioate is a primary alkyl group.

6. The lubricating composition of claim 3 characterized further in that each alkyl group of the zinc dialkylphosphorodithioate is a lower alkyl group.

8. A lubricating composition comprising a major amount of a lubricating oil and from about 0.01% to about 3.5% by Weight of an oxidation-inhibiting agent prepared by a process comprising treating an oil-soluble zinc dialkyl phosphorodithioate having a total of at least about 76 carbon atoms per phosphorus atom with from about 0.1 up to about 0.5 mole of a lower alkylene oxide having up to about 6 carbon atoms.

9. A lubricating composition of claim 8 characterized further in that the zinc dialkylphosphorodithioate is zine diprimary alkyl phosphorodithioate.

10. A lubricating composition of claim 8 characterized further in that the zinc dialkylphosphorodithioate is zinc diprimary-octyl phosphorodithioate.

'11. A lubricating composition of claim 8 characterized further in that the lower alkylene oxide is propylene oxide.

12. A lubricating composition comprising a major amount of a lubricating oil and from about 0.01% to about 3.5% by weight of an oxidation-inhibiting agent prepared by a process comprising treating a zinc di-primary-octylphosphorodithioate with about 0.5 mole of propylene oxide.

References Cited by the Examiner UNITED STATES PATENTS 2,496,508 2/50 Watson et a1 252-46] 2,914,478 11/59 Neif 25246.6 3,004,996 10/61 Arakelian et al. 25232.7

FOREIGN PATENTS 796,181 6/58 Great Britain. 819,169 8/59 Great Britain.

DANIEL E. WYMAN, Primary Examiner.

JOSEPH R. LIBERMAN, JULIUS GREENWALD,

Examiners. 

1. A LUBRICATING COMPOSITION COMPRISING A MAJOR AMOUNT OF LUBRICATING OIL AND FROM ABOUT 0.01 TO ABOUT 3.5% BY WEIGHT OF AN OXIDATION-INHIBITING AGENT PREPARED BY A PROCESS COMPRISING TREATING AN OIL-SOLUBLE GROUP II METAL SALT OF A PHOSPHOROTHIOIC ACID HAVING THE STRUCTURAL FORMULA 